The therapeutic use of antibodies has been recently approved. In fact, therapeutic imaging targets can be reached without allergic reactions. However, such procedures involve the intravenous injection of antibodies, which circulate throughout the body and hopefully attached to an antigen of a tumor, infection or site of scarring.
However, the ability to concentrate enough antibody at the target site is a problem. Antibodies are quite large molecules of complex, folded sequences of amino acids that have difficulty in penetrating the diseased tissue. The leakiness and varied vascularization and intralesional pressure of each type of tumor, infection or area of scarring due to ischemia will limit the application of antibody therapies. Antibodies that are hooked or linked to contrast imaging agents make an even larger molecule, which the further complicates the problem of penetration of the imaging or therapeutic agent into the tissue to be treated, i.e., target tissue. This problem results irrespective of whether the imaging agent is an isotope, a PET, an MRI, or a CT-type imaging agent. Further, this problem exists despite the different leakiness of different diseased tissues due to different disease entities.
With the advent of pulse inversion imaging, double resonance ultrasound imaging, and dual harmonic echo Doppler imaging, as well as 3-dimensional reconstruction, areas of imaging throughout the body for diagnosis and treatment can be satisfactorily obtained simultaneously if a contrast agent is use. Such ultrasound contrast agents typically contain an air or gas infiltrate core to increase reflectance of the diseased tissue to be studied.